Cephalometric analysis is the study of the dental and skeletal relationships for the head and is used by dentists and orthodontists as an assessment and planning tool for improved treatment of a patient. Conventional cephalometric analysis identifies bony and soft tissue landmarks in 2-D cephalometric radiographs in order to diagnose facial features and abnormalities prior to treatment, or to evaluate the progress of treatment.
For example, a dominant abnormality that can be identified in cephalometric analysis is the anteroposterior problem of malocclusion, relating to the skeletal relationship between the maxilla and mandible. Malocclusion is classified based on the relative position of the maxillary first molar. For Class I, neutrocclusion, the molar relationship is normal but other teeth may have problems such as spacing, crowding, or over- or under-eruption. For Class II, distocclusion, the mesiobuccal cusp of the maxillary first molar rests between the first mandible molar and second premolar. For Class III, mesiocclusion, the mesiobuccal cusp of the maxillary first molar is posterior to the mesiobuccal grooves of the mandibular first molar.
An exemplary conventional 2-D cephalometric analysis method described by Steiner in an article entitled “Cephalometrics in Clinical Practice” (paper read at the Charles H. Tweed Foundation for Orthodontic Research, October 1956, pp. 8-29) assesses maxilla and mandible in relation to the cranial base using angular measures. In the procedure described, Steiner selects four landmarks: Nasion, Point A, Point B and Sella. The Nasion is the intersection of the frontal bone and two nasal bones of the skull. Point A is regarded as the anterior limit of the apical base of the maxilla. Point B is regarded as the anterior limit of the apical base of the mandible. The Sella is at the mid-point of the sella turcica. The angle SNA (from Sella to Nasion, then to Point A) is used to determine if the maxilla is positioned anteriorly or posteriorly to the cranial base; a reading of about 82 degrees is regarded as normal. The angle SNB (from Sella to Nasion then to Point B) is used to determine if the mandible is positioned anteriorly or posteriorly to the cranial base; a reading of about 80 degrees is regarded as normal.
Recent studies in orthodontics indicate that there are persistent inaccuracies and inconsistencies in results provided using conventional 2-D cephalometric analysis. One notable study is entitled “In vivo comparison of conventional and cone beam CT synthesized cephalograms” by Vandana Kumar et al. in Angle Orthodontics, September 2008, pp. 873-879.
Due to fundamental limitations in data acquisition, conventional 2-D cephalometric analysis is focused primarily on aesthetics, without the concern of balance and symmetry about the human face. As stated in an article entitled “The human face as a 3D model for cephalometric analysis” by Treil et al. in World Journal of Orthodontics, pp. 1-6, plane geometry is inappropriate for analyzing anatomical volumes and their growth; only a 3-D diagnosis is able to suitably analyze the anatomical maxillofacial complex. The normal relationship has two more significant aspects: balance and symmetry, when balance and symmetry of the model are stable, these characteristics define what is normal for each person.
U.S. Pat. No. 6,879,712, entitled “System and method of digitally modeling craniofacial features for the purposes of diagnosis and treatment predictions” to Tuncay et al., discloses a method of generating a computer model of craniofacial features. The three-dimensional facial features data are acquired using laser scanning and digital photographs; dental features are acquired by physically modeling the teeth. The models are laser scanned. Skeletal features are then obtained from radiographs. The data are combined into a single computer model that can be manipulated and viewed in three dimensions. The model also has the ability for animation between the current modeled craniofacial features and theoretical craniofacial features.
U.S. Pat. No. 6,250,918, entitled “Method and apparatus for simulating tooth movement for an orthodontic patient” to Sachdeva et al., discloses a method of determining a 3-D direct path of movement from a 3-D digital model of an actual orthodontic structure and a 3-D model of a desired orthodontic structure. This method simulates tooth movement based on each tooth's corresponding three-dimensional direct path using laser scanned crown and markers on the tooth surface for scaling. There is no true whole tooth 3-D data using the method described.
Although significant strides have been made toward developing techniques that automate entry of measurements and computation of biometric data for craniofacial features based on such measurements, there is considerable room for improvement. Even with the benefit of existing tools, the practitioner requires sufficient training in order to use the biometric data effectively. The sizable amount of measured and calculated data complicates the task of developing and maintaining a treatment plan and can increase the risks of human oversight and error.
Thus it can be seen that there would be particular value in development of analysis utilities that generate and report cephalometric results that can help to direct treatment planning and to track patient progress at different stages of ongoing treatment.